Discharge device



July 26, 19.60 C, MQREHEAD 2,946,909

DISCHARGE DEVICE Filed March so, 19459 le 2o3o22I[ 1-2414225o|22o lo LMI.,

I6 32 28 36 34 :IIJ 26 34 36 2B 32 I8 WQEQM@ ATTORNEY s claims. (cl. 313-43),

This invention relates to electric discharge devices and,

more particularly, to fluorescent lamps intended to be operated under conditions of relatively high'loading and to a method of minimizing the loss of light output during the useful life of such lamps.' v l.

Y It is well-known that `the luminous eiciency of a nited States :Patent lluorescentlamp is largely determined by the amount of 2537 A. radiation which reaches the phosphor vcoating from. the mercury discharge.` rIt is also well-known that the intensity of 2537 A. radiation `reaches a peak vwhen the mercury-vapor pressure iswithin 'the range o f about 6 to 10 microns and that this pressure can 4be maintained by I the latter to increase resulting in a decrease in the intensity of the 2537 A. radiation and the lumen per watt eihciency of the lamp. 'It' has, accordingly, been impractical from an eciency standpoint merely to increase the loading of -a fluorescent lamp in an attempt to increase its. light output. In referring to` the loading of aV dated March 29, 1960, there is disclosed and claimed an improved heat shield and anode structure for an endcooled typehigh loaded lamp wherein by coating the aforesaid structure with black chrome-vanadium plating the lumen maintenance is greatly improved over control lamps made Without such plating.` Even with this im-A provement, however, the lumen maintenance performance of highly loaded iluorescent lamps is much poorer than that of'normally loaded lamps and thus disadvantageous from an eiiciency 'and lighting cost standpoint.

It is accordingly the general object of this invention to avoid and overcome the foregoing and other diliiculties of and objections to the prior art by the provision of a highly loaded iluorescent lamp wherein the loss of lumen output during life more nearly approaches that of standard uorescent lamps of normal loading.

' Theaforesaid object of the invention, and others which will become apparent as the description proceeds, are achieved by introducing a predetermined amount of nitrogen into a highly loaded fluorescent lamp the nonemissive portions of the mount structures whereof have been provided with black chrome-vanadium plating in accordance with the aforesaid U.S. Patent No. 2,930,919. The nitrogen is preferably mixed with the lill gas and introduced intoV the lamp during the gas-filling operation; For reasons not yet understood the combinationof the aforesaid black plating and nitnogen eifects an improvement in the lumen maintenance of a highly loaded lamp over and above that produced by the black plating alone and of approximately the same order yof magnitude as that effected by such plating over a conventional lamp of this character. The present invention accordingly constitutes an'improvement over the invention disclosed and claimed in the above-mentioned U.S. Patent No. 2,930,919.

For a better understanding of this invention Vreference should be had to the accompanying drawing wherein:

fluorescent lamp it is customary to express it interms of the number of Watts per unit of lamp length. Thus, a

standardw40 watt fluorescent lamp 4 ,feet in length is said to have a loading of 10 watts per foot. -Fluorescent lamps of conventional design having aloadng as high as.

16 wattsv per foot-are known but are lrelativelyinefficient n compared with lamps having the normal loading of 10 lwatts per foot and thus have not been widely adopted, at leastfin this country. Y, -Recently there have been developed highly loaded Vfluorescent lamps capable of operating at much higher loadings than the aforesaid upper limit of V16 Watts` per foot vheretofore employed in fluorescent lamps of standard desigm In these highly loadedlamp's the mercury-vapor pressure is controlled by providing a relatively cool region Within .the lamp whichhas a normal operating temperature within the required Vtemperature range off-40 C. to

45 C. This coolY region maybe created by shielding the outputjversus hours of operation drops'oif much faster Y with highly loaded lamps thankwith standard typefluorescent 'lanipsr4 Inl oopending. application1 ,Serial No. 786,993, led JanuarylS, 1959, by PnWainio` and owned by the present assignee, now U.S. Patent No. 2,930,919,

Fig.- l is an elevational view, partly in section, Yof one type of highly loaded fluorescent lamp in which the present can be advantageously employed;

Fig. 2 is an enlarged sectional view along the line II-II of Fig. l, in the direction of the arrows;

Fig. 3 is an enlarged perspective view of the electrode and shield portionlof a mount for the l-amp shown in Fig. 1, illustrating in further detail the plated heat shield, lead-in conductors and enlarged anodes; and

Fig. V4 is another form of highly loaded fluorescent lamps in which this invention can be incorporated.

With specific reference .to the form of the invention illustrated in the drawing, the lamp 10 in Fig. l comprises a tubular envelope l2 which carries a phosphor coating 14 on its inner surfaces and encloses an inert, ionizable starting gas such as a mixture of 20% argon-80% neon at a pressure of about 2 mm. land a small charge of mercury 16. At each end of the envelope 12 is provided a mount 18 comprising the usual re-entrant stem 20 having a press portion 30 through which is'sealed a pair of lead-in conductors 22. The ends of the lead-in conductors 22 which extend inwardly into the envelope 12 are electrically connected to and carry enlarged L-shaped anodes 26 arranged to form a rectangular enclosure, as shown more particularlyin Figs. Zand 3. Electrodes 2li-,such as coiled-coil tungsten filaments iilled with a Y conventional mixture of alkaline-earth oxides are attached toand Vsupported between the inner ends of thelead-in conductors 22 Yand are centrally disposed within the enclosure formed by the Venlarged anodes 26, in accordancewith the usual practice. Metallic heat shields-28 are aiixed to the press portions 30 of each stem 20 proximate the associated end of the envelope 12 and closer thereto than the electrodes 24. The heat shields 28 are considerably-smaller in diameter than the envelope-12 l to permit the gas to circulate freely and thereby provides a s 2,946,909 v e cooling chamber 32 at each end of the envelope 12 adapted to maintain the operating mercury-vapor pressure wlthin the desired 6 to 10 micron range, as is well-known in the art. Each of the heat shields 28 is provided with a tab 34 which is electrically connected with one of the lead-in conductors 22 that support each of the electrodes 24 so that said heat shields also serve as anode surfaces. yIn accordance with the present invention at least the enlarged anodes 26 and heat shields 28 are provided with a black chrome-vanadium plating or coating 36 and nitrogen within the range of .3% to 3% by volume is added to the lill gas normally introduced into the lamp `during manufacture. A plating of the aforesaid character is disclosed in copending application Serial No. 591,206 led lune 13, 1956, by Wainio and Sutter, now U`.S. Patent No. 2,885,587, owned by the present assignee. A similar plating is also disclosed in U. S. Patent No. 2,824,829 dated February 25, 1958. The black chromevanadium plating can be applied to the anodes 26 and heat shields 28 in the manner youtlined in detail in the aforesaid Patent No. 2,885,587. Briefly, this plating 36 is formed of chromium, vanadium and oxygen in which there are from 100 to 9.5 parts by Weight of total chromium per part by weight of vanadium with the vanadium in the plating essentially compounded as vanadium trioxide. The chromium in the plating is partially oxidized with the ratio of total chromium atoms to total oxygen atoms combined with chromium in the plating being from 2:1 to 100:1. The thickness of the plating is not critical although the exterior surfaces of the anodes 26 and shields 28 should be completely covered. As an example, the coating can have a thickness of about 0.05 mil. The surfaces of the plating adjacent the base metal forming the anodes and shields may tend 'to interact slightly with the base metal to form a complex compound, but the bulk of the plating including all exposed portions remains unreacted with the base metal.

The nitrogen is preferably mixed with the ll gas andv introduced into the lamp during the gas-filling operation so as not to interfere with normal sequence of opera# tions followed in fabricating the lamp. It can, however, be introduced separately before or after the lamp has been charged with the fill gas normally employed. Any snitable noble gas or mixture thereof may be employed along with the nitrogen, as for example argon, 7% krypton- 93% neon or 10% helium-90% argon. The most pronounced improvement in lumen maintenance has been obtained when nitrogen is added within the range of about .5% to 1.5% with optimum results being achieved with addition of 1% nitrogen. Upon seasoning the com@ pleted lamp 10 the nitrogen essentially disappears from the gas phase and the till gas is restored to its original noble gas constituents. The exact form in which the nitrogen is still present within the seasoned lamp and the mechanism by which the nitrogen effects the resultant improvement in the lumen maintenance thereof is not known at the present time. It is theorized, however, that due to the increase in 1850 A. radiation incident with the increase in the lamp loading the halophosphate type phosphor customarily employed in fluorescent lamps deterioratesy or is otherwise deleterioiusly affected at a faster rate than heretofore. It is further theorized that because of the presence of the above-specified black chrome-vanadium plating the nitrogen is allowedrto react with the mercury-vapor to form mercury nitride or some other mercury complex which inhibits in some manner the deterioration of the halophosphate phosphor coating 14 and establishes a beneficial nitrogen cycle within the finished lamp. Whatever the reason, it is a denitely established fact that the combination of nitrogen within the range of .3% to 3% and black chromevanadium plating on at least the enlarged anodes 26 and shields 28 effects a marked improvement in the `lumen maintenance of highly loaded lamps employing conventional halophcsphate type phosphorsywhich phosphors are well-known and described in U.S. Patent No. 2,488,733 dated November 22, 1949. As will be obvious, small amounts of other types of phosphors such as greenemitting zinc silicate or blue-ernitting calcium tungstate may be added to the halophosphate phosphor to comprise the coating -14 and thereby adjust the color of the light output without materially effecting the degree of improvement obtained in lumen maintenance.

The lumen maintenance of a control group of lamps having unplated lead-in conductors, anodes and shields and another group having the aforesaid parts coated with black chrome-vanadium plating were compared with otherwise-identical lamps incorporating both the black plating and nitrogen addition to the fill gas in accordance with this invention. The lamps were designed to operate at a loading of 25 watts per foot, had an overall length of 4 feet and an O.D. of 11/2 inches and had nickel anodes, heat shields and inner lead-conductors. After 500 hours of operation the control lamps without the black plating or nitrogen displayed a light output which was approximately 83% of the light output measured at 100 hours operation. After the same 500 hours period of operation the other group of control lamps incorporating the yblack chrome-vanadium plating on the shields, leadin conductors and anodes displayed a light output which was approximately 88% of the light output as measured at 100 hours operation. In contrast, lamps manufactured in accordance with this invention and having both the black plating and a 1% nitrogen addition to the till gas displayed a light output approximately 92% of the light output as measured at 100'hours operation and comparable lamps with 2% nitrogen addition gave 89% of the 100-hour light output after 500 hours burning. Due to the variations in light output incident with the first 100 hours of operation the 100-hour value has been used for rating purposes as is customary in the art. The aforesaid comparative test data are listed in the following table, designated Table I:

As will be noted, the use of a 1% nitrogen addition to the ll gas and black chrome-vanadium plating on the non-emissive metallic portions of 'the mount structure produced at least a 41/z% improvement in maintained lumen output after 500 hours operation over the control group lamps incorporatingonly the black plating and at least lOl/2% improvement over the control group of lamps without such plating. For this particular size of lamp this represents a gain in light output of about 240 lumens and 540 lumens, respectively, during the first 500 hours of operation. Of equal importance, the addition of nitrogen unexpectedly inhibited the rate at which the light output dropped after the first 500 hours, as evidenced by the fact that after 1000 hours operation the control lamps with only black plated parts had a light output equivalent to only 77% of the 100-hour value Whereas lamps having a 1% nitrogen addition and black plating had a light output of the 100-hour value that is, an overall improvement of over 10% or an additional improvementin maintained lumen output 5 at 1000 hours of at least Vz% compared to that exhibited after 500 hours burning. The foregoing performance ligures were obtained 4from highly loaded uorescent lamps wherein the blaclt chrome-vanadium plating 36 was applied to the enlarged anodes 26, heat shields 28 and .to the inwardly-extending portions of the lead-in conductors 22 that is, tothe non-emissive metallic portions of the mounts 18. If desired, the plating 36 may be omitted from the lead-in conductors 22 in which case the improvement in the maintenance of light output will be slightly decreased but will still be significantly better than either group of control lamps.

The invention may be also advantageously employed in a highly loaded fluorescent lamp 10a identical in construction with the end-cooled type lamp above-described except that the desired cooling efrect is achieved by means of a protrusion 38 at the center of the lamp envelope 12a rather than by end cooling chambers. In this type lamp the heat shields are accordingly eliminated and the lamp mounts proportionately decreased in length. As a speciiic example lamps of this type may have a loading of 25 Watts per foot, an envelope 12a approximately 5 feet long and approximately 1% inches in diameter, and a protrusion 38 about 1%2 of an inch y in diameter and about 13/32 of an inch long.

It will be recognized that the objects of the invention have been achieved by providing a norescent lamp which is adapted to be operated at relatively high loadings with a lumen maintenance which is not only significantly better than that heretofore obtained with similar lamps but which approaches that of normally loaded lamps. Y

While two best-known embodiments have Ybeenillustrated and described in detail,it is to be particularly understood that the invention is not limited thereto or thereby.

and extending inwardly into said envelope, a mount structure at each end of said envelope including electrodes carried by said lead-in conductors, means comprising an integral part of saidvlamp for controlling the mercuryvapor pressure when said lamp is normally operated, and a black chromium-vanadium plating on the non-emissive portions of each of said mount structures.

2. A uorescent lamp adapted when normally operated to have a loading in'excess of 16 watts per foot compris- Y to have a loading lin excess of 16 watts per foot comprisy ing, an elongated envelope having a small charge of mer- 1 ing, an envelope having a small charge of mercury sealed therein, a phosphor coating on the inner surface of said envelope comprising a halophosphate phosphona gaseous filling within said envelope initially comprising a mixture o-- at least one inert ionizable gas and nitrogen wherein the nitrogen is within the :range of .5% Ito 1.5% by volume, lead-in conductors sealed through and extending inwardly into said envelope, `electrodes connected to said lead-in conductors, enlarged anodes positioned proximate said electrodes and electrically connected to said lead-in conductors, means comprising an integral part of Y said lamp for controlling the mercury-vapor pressure when sa-id llamp is normally operated, Vand a black` chromium-vanadium plating on said enlarged anodes, said plating principally comprising from 100to79a5 Yparts 'by weight of total chromium per part by weight of vanadium, the vanadium in said plating essentially compounded as V203, and the chromium in said plating partially oxidized V,atoms combined from 2:1 to'100:1.

with `the ratio of `total chromium atoms to total oxygen from 2:1 to 100::1. I n

. 3A. A fluorescent lamp adapted when normally operated to have a loading in excess of 16 watts per foot comprising, an elongated envelope having a small charge of mercury sealed therein,.a phosphor coating on the inner surface of said envelope comprising a halophosphate phosphor, a gaseous filling Within said envelope initially co-mprising a mixture of at least one inert ionizable gas and nitrogen wherein the nitrogen is within the range of .3% to 3% by volume, lead-in conductors sealed through and extending inwardly from each end of said envelope, electrodes connected to said lead-in conductors, enlarged anodes positioned proximate said electrodes and electrically connecting with said lead-in conductors, metallic heat-deflecting shields proximate each end of said envelope and positioned closer to the ends of said envelope than said electrodes to form cooling chambers thereat, each of said shields electrically connecting with one of the lead-in conductors connected to each of said electrodes, and a black chromium-vanadium plating on said enlarged anodes and heat shields, said plating principally comprising from 100 to 9;5 parts by Weight of a total chromium per part by weight of vanadium, the vanadium in said plating essentially compounded as V203, `and the chromium lin said plating partially oxidized with the ratio of total chromium atoms to total oxygen atoms f combined with chromiumV in said plating being from 2:1 to 100:1.v

4. A lluorescent lamp adapted when normally operated cury vsealed therein, a phosphor coating on the inner surface of said envelope comprising a halophosphate phosphor, a gaseous filling within said envelope initially comprising a mixture of at least one inert ionizable gas and nitrogen wherein the nitrogen .is withinthe range of .3% to 3% by volume, lead-in conductors'sealed through and extending v inwardly from each end of said envelope, electrodes connected to said lead-in conductors, enlarged anodes positioned proximate sa-id electrodes and electrically connecting with said lead-in conductors, means comprising an integral part of the Wall of said envelope for controlling `the mercury vapor'pressure during normal operation of said lamp, and a black chromiumvanadium plating on said enlarged anodes, said plating principally comprising from 100 to 9.5 parts by Weight of total chromium per part by Weight of vanadium, the. vanadium fin said plating essentially compounded as V203, and the chromium in said plating partially oxidized Y with .the ratio of total chromium atoms to total oxygen with chromium in said plating being 5. A fluorescent lamp adapted when normally operated to have a loading in excessV of 16 watts per foot comprising, an elongatedV envelope having a small charge of 'mercury sealed therein, a phosphor coating'on the inner surface of s'aid envelope comprising a halophosphate phosphor, a` gaseous lling lwithin said envelope initially comprising a mixture of at least oneinent ionizable gas and nitrogen wherein the nitrogen is within the vv'range'of .5%

-to 1.5 by volume, lead-in conductors sealed through ly` connecting with said lead-in conductors, metallic heat- Y e deecting shields proximate each end'of said envelope `offsaid shields electrically connecting with one of .the

Y lead-in conductors connected-to each of said electrodes,

kReferences Cited in the le of this patent UNITED STATES PATENTS Geyer Oct. 24, 1950 May Jan.l 8, 1957 Mistler V V Feb. 18, 1958 Wainio et al. May l5, 1959 Fraser June 30, 1959 

